Examples of this type of conventional illumination device can include the “bulb-type lamp” disclosed in Japanese Patent Application Laid-Open No. 2011-146253 (or US2013/0114253A1 corresponding thereto), which is illustrated in FIG. 1.
That is, a polygonal support member 81 is attached to a tip of one end of a heat pipe 80, and a plurality of light emitting modules 83 are attached to the surface of the support member 81 (six faces of the peripheral side and one face of the top thereof) via a heat dissipation sheet. The light emitting modules 83 each can include a substrate 84 and a semiconductor light emitting element or LED element 85 mounted on the substrate 84. Then, a dome-shaped globe 86 having light diffusion properties is formed to cover the support member 81 and the light emitting modules 83, which together constitute a light emission body 87. It is said that the thus formed bulb-type lamp 88 can have light distribution characteristics similar to an incandescent bulb.
Japanese Patent No. 4689762 discloses an illumination device referred to as an “LED bulb” of this type, which can include an optical system as illustrated in (a) of FIG. 2.
The disclosed LED bulb can include an LED light emitting element 90 and a reflecting member 91 disposed forward of the LED light emitting element 90 in its light illumination direction. The reflecting member 91 can include a reflecting surface 95 configured to face to the light emission surface 92 of the LED light emitting element 90 and having a center axis 96. The reflecting surface 95 can be composed of an apex 93 projecting toward the light emission surface 92 of the LED light emitting element 90, and a curved conical reflecting surface 94 that is a side surface extending from the apex 93 and curved while being concave toward the center axis 96.
With this configuration, the light emitted from the LED light emitting element 90 can be radially reflected sideward and obliquely rearward with respect to the light illumination direction by means of the curved conical reflecting surface 94 of the reflecting member 91. Then the curved conical reflecting surface 94 can form a pseud light source (E) by the reflected light (F) therefrom. According to the conventional light source device disclosed in the conventional art, the light emission direction of light from the pseud light source (E) can be substantially the same as the light emission direction of light from a halogen bulb light source with a filament. Consequently, the formed position and the size of the light emission region of the pseud light source (E) can be the same as those of such a halogen bulb.
Referring back to FIG. 1, the bulb-type lamp 88 of Japanese Patent Application Laid-Open No. 2011-146253 includes a plurality of the LED elements 85 disposed on the support member 81 in a scattered manner, and the LED elements 85 each can be considered as a point light source in an optical system. Accordingly, there arises a problem in which the optical system having a single focal point cannot accurately control the light distribution of the light emitted from any LED elements other than one LED element just disposed at the focal point of the optical system.
Furthermore, in the LED bulb disclosed in Japanese Patent No. 4689762, the light from the pseud light source (E) can be reflected by the curved conical reflecting surface 94, so that the reflected light (D) can form the light distribution pattern 97 as illustrated in (b) of FIG. 2 with a curved conical shape projected by the curved conical reflecting surface 94. The light emitted from the pseud light source (E) can thus form light distribution characteristics and luminance distribution different from those of light emitted from a coiled filament with a constant diameter.
In other words, the light distribution characteristics of the pseud light source (E) can correspond to those of a coiled filament (F) that is prepared by winding filament while gradually changing the winding diameter to form a curved conical shape. Therefore, the pseud light source (E) can emit light rays including first light rays emitted from first portions corresponding to those of filament wound with larger diameters and second light rays emitted from second portions corresponding to those of filament wound with smaller diameters. When such a pseud light source (E) is mounted within a lighting fixture having a light distribution control system, the first light rays from the first portions of the pseud light source (E) can be controlled to provide light distribution characteristics in such a manner that they are spread by the light distribution control system while the second light rays from the second portions thereof can be controlled to provide light distribution characteristics in such a manner that they are converged to a certain direction.
As a result, the lighting fixture with such a pseud light source (E) installed in position is difficult to obtain the same or similar light distribution characteristics as or to those of a conventional lighting fixture including a coiled filament with a constant diameter.
Furthermore, the reflecting member 91 having the curved conical reflecting surface 94 that can provide such a pseud light source (E) needs to be supported by a support, and such a support must be arranged in the vicinity of the reflecting member 91 due to the limited space within the lighting fixture. This, however, results in formation of a shadow by the support shielding the light emitted from the pseud light source (E).